David Cameron has insisted the Government is doing everything it can to get hundreds of British nationals out of Libya as the country descends further into violence and bloodshed.

Fears were growing for up to 170 UK oil workers stranded in remote and highly vulnerable desert locations across the North African state.

The latest charter plane evacuating dozens of Britons from the capital, Tripoli, left for Gatwick at 4.30pm on Friday, carrying 79 passengers including 34 Britons. Another charter flight will depart from Tripoli on Saturday, which the Foreign Office said was likely to be the last.

The Foreign Office believes up to 500 UK nationals could still be in the country in total. The Prime Minister urged them to "leave now". The security situation around Tripoli has been deteriorating as fighting between supporters and opponents of dictator Colonel Muammar Gaddafi has escalated.

Mr Cameron said there would be more flights made available as necessary and that a second Royal Navy ship, HMS York, was being deployed to the area. HMS Cumberland, which left second city Benghazi with 68 Britons on Thursday, is set to return after docking in Malta. Its voyage has been delayed by poor conditions at sea.

Those Britons who have returned to the UK brought with them tales of ever-deepening chaos and of the terror of being stranded in oilfield camps threatened by roaming militias.

After heavy criticism that the Government's response to the crisis has been slow and shambolic, Mr Cameron chaired emergency planning meetings with senior ministers and security advisers.

"We will do everything we can today and tomorrow to help those people and planning is under way to do just that," the Prime Minister said on Friday. "I would say that people do need to leave now and that is the message that I give very strongly to British citizens in Libya. For those in the desert, we will do everything we can and we are active on that right now to help get you out."

Labour leader Ed Miliband said there was "a worrying whiff of incompetence" about the Government's handling of the situation. He said: "Frankly, I think Mr Cameron has got to get a grip on the way this Government works.

"Clearly the Government should have acted earlier to make flights available so that people could come home. Now they have just got to move as quickly as possible and get as many flights out there as possible so that British citizens who obviously want to come home, and want to get out of the situation they find themselves in Libya, can come back to the UK."